This invention relates to locking devices. More particularly, but not exclusively, the invention relates to locking devices for locking rotary compressor blades to the rotary discs upon which the blades are mounted.
In some high pressure axial flow compressors, the blades are retained in circumferential grooves in the rim of the compressor disc. In order to prevent the blades moving around the disc, one or more locking devices are provided in the groove or grooves.
A problem with such locking devices is that the temperatures and stresses experienced in use of a gas turbine engine can result in the locking devices seizing in the groove. During servicing of the engine, it is often necessary to dismantle the compressor, which means that the seized locking devices need to be drilled out which can result in damage to the disc.
According to one aspect of this invention there is provided a locking device for locking a first article in a recess of a second article, the device being securable in a secured condition in said recess to lock the first article to the second article, the device comprising a weakness, whereby a force can be applied to said locking device to break the device at said weakness to release the device from said secured condition thereby allowing the first article to be removed from the second article.
The preferred embodiment of this invention is particularly suitable for use in preventing circumferential movement of first article, in the form of compressor or turbine blades of a gas turbine engine, around a second article comprising a support member in the form of a disc on which the blades are mounted.
The locking device may include a body member and securing means to secure the locking device to the second article wherein the weakness extends across a region of at least one of the body member and the securing means.
Preferably at least one of the securing means and the body member comprises first and second portions, wherein the weakness extends between the first and second portions of one of the body member and the securing means. The force may be applied to effect relative turning movement of said first portion relative to said second portion to cause the first portion to shear relative to the second portion at said weakness and to separate therefrom.
The body member may define a bore extending therethrough and the securing means may include an elongate member to extend through the bore to engage the second article, thereby securing the locking device against the second article.
In a first embodiment, the body member includes said first and second portions and said weakened region. The securing means may be securable to said body member at said first portion. The elongate member may extend through the region of the bore through the second portion to engage the second article.
The weakened region may extend at least partially around the body member, preferably substantially wholly therearound. The weakened region may define a boundary between the first and second portions and may comprise a groove or concavity.
Alternatively, or in addition, at least a part of the bore through the region of the second portion adjacent the first portion may be wider than the bore extending through the first portion to create the weakened region at the junction of said first and second portions. Preferably, the wider portion of the bore extends from the first portion to the adjacent end of the bore in the second portion.
Conveniently, the securing member is generally cylindrical in configuration and may be in the form of a bolt or a screw, suitably a grub screw.
In a second embodiment, the securing means includes said first and second portions, and said weakness. The first portion may include said elongate member which may extend through the second portion. The second portion is preferably engageable with the body member. The second portion is preferably engageable with the body member. The second portion and the body member may be provided with threads to co-operate with each other. Preferably, the threads on the body member are internal threads within the bore.
The region of weakness may extend at least partially around the securing means, and preferably substantially wholly therearound.
The first portion may be receivable in an indentation in the first article, for example, in a root shroud of an adjacent rotor blade. The first portion is preferably configured and/or sized to enable the first portion to be turned relative to the first article. Conveniently the first portion is of a substantially circular cross-section, or may be any other suitable configuration, for example, triangular or hexagonal, to allow a torque applying device, e.g. a spanner, to be applied thereto to turn the first portion relative to the second portion.
The body member may be shaped to be received in the recess which may be a groove extending circumferentially around said support member. The second article may include flange means extending partially over and spaced from the base of the recess, the second portion of said body member being adapted to engage the flange means when the device is located in the recess and the securing means actuated to lock the device to the second article.
Preferably complementary threads are formed on the part of said bore extending through the body member, and on a corresponding part of the securing means. In the first embodiment, the threaded parts of the bore and of the securing member are on regions thereof which are radially outwardly located in use.
According to another aspect of this invention there is provided a rotor assembly for a gas turbine engine, the rotor assembly including a plurality of rotor blades assembled on a rotor disc, and at least one locking device as described above engaged with a groove in the disc, wherein each rotor blade located adjacent the, or each, locking device defines an indentation to receive a part of the first portion of said body member therein, the indentation being configured and/or sized to allow the first portion to turn relative to the second portion. The indentations of adjacent blades may together define an access aperture for the locking device. Conveniently, the aperture defined by a pair of adjacent blades is substantially circular. In the preferred embodiment, the invention defined in each of said adjacent blades is substantially semi-circular.